This invention relates generally to the controlling of dust concentration levels in a room within which dust-releasing equipment is housed and relates, more particularly, to the means and methods for controlling the concentration levels of respirable dust in a machine room within which a papermaking machine is housed.
The processes and systems with which this invention is to be compared include those used for ventilating the environment of a room within which dust is generated and within which operators are expected to work. In a room in which a papermaking machine is used for making tissue, for example, a relatively large amount of dust (including cellulose fiber, clay, starch and other chemical dust) is released into the surrounding air by the papermaking process, and this dust can create operating hazards, worker health hazards, and is likely to migrate to various areas of the room and create a cleanliness (e.g. machine hygiene) problem or increase the risk of fire at those areas.
Heretofore, attempts to control the amount of dust released into a papermaking machine room involve the capturing of dust at the source of creation (referred to herein as primary dust control) and the containing of dust adjacent the source of dust creation (referred to herein as secondary dust control). Primary dust control systems can include equipment known in the art as "on sheet" dust collectors or any equipment designed to remove dust from its point of generation, and secondary dust control schemes can include canopy hoods, area dust collectors, winder enclosures and specially-designed air curtain systems for containing dust near its point of generation. However, no primary and secondary dust control systems are totally effective in preventing the release of all unwanted dust into the environment of a machine room.
Conventional schemes used for ventilating a paper-making room commonly involve the ventilating of the room so that fresh air continually replenishes the air surrounding the machine into which dust is released. However, the fresh air which is introduced into the room in accordance with these conventional schemes is normally introduced therein at a relatively high velocity and in such a manner that regions of air within the room are "entrained" by the flow of fresh air, and this entrainment of air establishes uncontrolled reverse migration air flow patterns which result in a mass dilution, or mixing, of the fresh air with dust-laden air in the room. Consequently, the likelihood is high with these conventional room-ventilation schemes that few, if any, locations will exist within the room which is appreciably free from some degree of dust and that dust-laden air will be present in areas of the room where it could be breathed by operators. To protect operators who work in such papermaking machine environments, governmental regulations have been established which require that the concentration levels of respirable dust in a room be maintained below prescribed levels.
In addition to the release of dust, a papermaking process also releases a relatively large amount of heat and humidity-creating vapor into the surrounding air. Of course, inasmuch as common room-ventilating schemes mix incoming fresh air with dust-carrying air, the heat and humidity-creating vapors released by the papermaking process are mixed with the fresh air, as well. Prior art (i.e. conventional) air systems can therefore lead to uncontrolled and uneven temperatures and humidity areas within the machine room.
It is an object of the present invention to provide a new and improved process and system for ventilating the room within which dust-releasing equipment is located.
Another object of the present invention is to provide such a process and system for reducing the concentration levels of dust in areas adjacent the dust-releasing equipment.
Still another object of the present invention is to provide such a process and system whose operation controls the migration pattern of dust-carrying air through the room so that fresh air which is directed into the environment of the room displaces, rather than is diluted by, the dust-carrying air in the room.
Yet another object of the present invention is to provide such a process and system which is particularly well-suited for use in a room within which a papermaking machine, such as a tissue-making machine, is housed for limiting the concentration levels of dust in areas of the room adjacent the tissue-making machine and controlling the concentration levels of heat and vapors which are released by the tissue-making machine during operation.